1. Field of the Invention
This invention relates to a magnetic tape cassette and, more particularly, relates to a magnetic tape cassette suitable for use for recording a digital signal, for example, a PCM (pulse-code modulated) signal.
2. Description of the Prior Art
At present, a PCM recording and reproducing apparatus has been proposed in which an analog signal such as an audio signal or the like is converted into a digital signal, for example, a PCM signal and then recorded on (or reproduced from) a magnetic tape. In the known PCM recording and reproducing apparatus, there is such one which uses a rotary head to make a relatively high recording density. In such PCM recording and reproducing apparatus having the rotary head, upon recording (or reproducing), a magnetic tape is drawn out from the tape cassette, wound around the rotary drum in which the rotary head is provided, and then the recording (or reproducing) is carried out.
In the tape cassette incorporating therein such magnetic tape, if oil component such as fingerprints or the like and dusts adhere to the magnetic tape, a dropout is caused in the reproduced signal. So, in order to prevent the oil component such as fingerprints or the like and dusts from adhering to the magnetic tape, the magnetic tape has to be held in a closed state as tightly as possible. Moreover, it is necessary to provide a space in front of the tape cassette through which a tape guide system is inserted into the tape cassette for drawing out the magnetic tape from the tape cassette upon recording (or reproducing).
Therefore, such a tape cassette as shown in FIGS. 1 and 2 is proposed. In FIGS. 1 and 2, reference numeral generally designates a cassette casing and this cassette casing 1 consists of a pair of an upper half 2 and a lower half 3 which are formed integral by screw bolts (not shown). Reference numeral 2a designates a transparent window plate provided on the upper surface portion of the upper half 2. Reference numerals 4a and 4b designate a pair of reel hubs which are incorporated into the cassette casing 1 and rotatably engaged with a pair of reel shaft insertion apertures 5a and 5b which are formed through the lower half 3 at its predetermined positions. A magnetic tape 6 is wound around the pair of reel hubs 4a and 4b. Reference numerals 7a and 7b respectively designate tape guide columns which are planted on the lower half 3 facing the front portion of the tape cassette near the right and left side wall portions. The magnetic tape 6 is stretched between and in contact with the tape guide columns 7a and 7b so as to be capable of running at a predetermined position of the front portion of the tape cassette. Reference numeral 3a designates a cut-out portion formed through the lower half 3 over a predetermined width in a rectangular shape at the portion opposing the rear surface of the magnetic tape 6 stretched between the tape guide columns 7a and 7b. Upon recording (or reproducing), inserted into this cut-out portion 3a is a tape guide system which is adapted to draw out the magnetic tape 6 and provided in the recording and reproducing apparatus though not shown.
Reference numeral 8 designates a front lid which is rotatably pivoted to the cassette casing 1 at its front side through its arm portions 8a and 8b which are formed at the both sides thereof. This front lid 8 is adapted to open and/or close the front portion of the cassette casing 1.
Reference numeral 9 designates a slider or sliding member of nearly U-shape which is provided such that it can be slidably moved back and forth in opposing relation to the lower surface and right and left side wall portions of the lower half 3. Reference numerals 9a and 9b respectively designate reel shaft insertion corresponding apertures which are bored through the sliding member 9 at such positions that when the sliding member 9 is slidably moved backward so as to expose the cut-out portion 3a, they correspond to the reel shaft insertion apertures 5a and 5b, respectively. Reference numerals 10a and 10b respectively designate positioning holes which are formed from the lower surface portion of the lower half 3 in correspondence with the tape guide columns 7a and 7b.
In such magnetic tape cassette, upon non-use, as shown in FIG. 1, the front portion of the cassette casing 1 is closed by the front lid 8 and the sliding member 9 is slidably moved forward so that the cut-out portion 3a, the reel shaft insertion apertures 5a, 5b and the positioning holes 10a, 10b are closed by the sliding member 9, thus the magnetic tape 6 being tightly shielded within the cassette casing 1.
Upon use, as shown in FIG. 2, the sliding member 9 is slidably moved backward to open the cut-out portion 3a, the reel shaft insertion apertures 5a, 5b and the positioning holes 10a, 10b. And, the front lid 8 is rotated upward to expose the magnetic tape 6 at the front portion of the cassette casing 1 and the tape guide system, the reel shafts and the positioning protrusions are respectively inserted into the cut-out portion 3a, the reel shaft insertion apertures 5a, 5b and the positioning holes 10a, 10b so that the magnetic tape 6 is drawn forward from the front portion of the cassette casing 1 by the tape guide system and loaded onto the rotary drum so as to carry out the predetermined recording (or reproducing).
By the way, the magnetic tape 6 loaded in such magnetic tape cassette is opposed at its magnetic surface to the front lid 8. Therefore, it is desired that upon non-use, the front lid 8 can be prevented from being rotated unintentionally so as not to open the front portion of the cassette casing 1 by a simple operation.